Outdoors: Monarchs begin journey to Mexico over the winter

Friday

Aug 30, 2013 at 6:00 AM

Mark Blazis Outdoors

The four monarchs I saw crossing Cape Cod Bay this week looked much out of place as they fluttered clumsily over bluefish far from their natal milkweed patches. Two miles out at sea, with nothing to feed or rest on, they were beginning their seemingly impossible marathon to Mexico to over winter.

The fabulous four were distant descendants of adults (great, great, great grandparents) that left Mexico last winter, laid eggs in milkweed patches as they flew a short distance north — and died. Their fast-developing progeny hatched, matured and continued the many-legged journey, finding other milkweed patches farther north — and dying. The next couple generations similarly continued north, genetically destined to finally reach us — and die here. Only the last generation born late this year will survive to fly over land and sea all the way back to Mexico to complete the yearly cycle. But many perils lay ahead of them.

Feeding on milkweed — a plant toxic to many other species — they uniquely acquire a protection against birds which learn that the monarch caterpillar's black, orange, and white pattern means eat-and-die. If only the monarch's color could afford them immunity against their other threats.

Although monarch numbers can vary greatly from year to year in local patches, the population for 2013 seems to be lower than normal almost everywhere one looks throughout the Northeast and Canada. Lepidopterists are concerned.

Their greatest threat is on their wintering grounds in Mexico, where they hibernate on just a few uniquely suitable mountains. While at best we can normally hope to see a hundred of the colorful sprites on any given late August or early September day here, they'll soon be funneling through Texas in vast numbers. On a deer stand near San Angelo a few Septembers back, I watched in amazement as a constant stream of countless monarchs flew by me, all flitting spritely toward the border as the sun lowered.

By November, the Mexican high-altitude forests they arrive at should be stunningly colored by their presence. The spectacle should rival or even surpass our fall foliage. But the colors are dimming — and have been for some time. Monarchs' wintering numbers last year were at their lowest point in 20 years. Something's drastically wrong with the habitat and conditions they need to survive.

Not long ago, about a dozen Mexican colonies in those mountains had densities averaging over 20 million per acre. Last year, the wintering area occupied by them had diminished by more than 50 percent. Their forests are being cut down by timber interests. And their problem isn't limited to an unenlightened Mexico.

Here in America, the wild plants monarchs need to survive on are diminishing. Heat and drought continued to take their toll on monarchs again across America this year. The delicate butterflies don't readily tolerate extreme temperature and precipitation fluctuations. Global warming is hitting them hard. Human development and agricultural practices exacerbate their stress, too. Less milkweed is available to them in our intensely managed corn belt and manicured suburbia. Less available food means less fat accumulation for them to survive their great migration and endure their cold and often frosty hibernation period.

In addition, just as herbicides are implicated in the demise of our honeybees, the potent chemicals seem to also be taking their toll on monarchs. As milkweed is toxic to livestock, farmers are spraying massive areas of fields to eradicate them.

The development of crops that can withstand the spraying increases their usage. Essential milkweed foliage and nectar are being significantly eliminated. From 2009-10, spraying has eliminated over half the previously available milkweed in agricultural areas, depleting the butterfly's population by 80 percent there.

The monarchs' secret wintering grounds remained a mystery until their amazing discovery in the coniferous forests of central Mexico's high-altitude mountains in 1975. The discoverers were overwhelmed by the massive spectacle of their stunning color.

Unfortunately, the trees that are critical to their survival during their dormancy, providing them with an insulating umbrella against rain and frost, are being cut for timber. Their sanctuary of pine/fir forest is about 10 degrees warmer than the open areas outside it, so the monarchs cluster tightly together in the arboreal vegetation — whatever remains of it. Without the trees' protection from the elements, monarchs die off in massive numbers, carpeting the sparse forest floor below. Without greater protection from loggers, monarchs will decline even more.

While monarchs exist elsewhere in the world and are therefore not considered globally threatened, our unique migratory population could quite easily disappear if we're not careful. Losing such an amazing faunal icon is unacceptable.

The monarchs that we see now returning to Mexico incredibly are three to five generations beyond the individuals that left the Mexican mountain forests last spring. They've never been to Mexico before. How they know where to precisely migrate without GPS is part of the magic of genetic instinct.

Equally astounding is the August generation's ability to make the entire great odyssey back to Mexico, over-winter, migrate north a bit, and breed. What's in their late-season milkweed and changing sunshine levels that allows just their age/class to accomplish this feat? They are a marvel of surprising strength and fragility.

Some concerned naturalists are planting milkweed and other nectar sources along their migration route. The monarch's beauty is one good reason why some of us refuse to use pesticides and don't turn all of our property into monocultures of sterile, lifeless lawn. If you can, leave some of your property wild for them and encourage milkweed growth. But efforts to save the monarch will be for naught unless Americans better preserve their milkweed habitat and Mexicans preserve their pine forests. And even those efforts may not be enough if we don't mitigate global warming.